In order that a long term evolution (LTE) system can acquire a greater transmission bandwidth from limited spectrum resource, a co-frequency networking technology is generally used to improve spectrum utilization in the LTE system. A coordinated multiple points (CoMP) transmission technology is one of the common co-frequency networking technologies.
The CoMP transmission means that multiple transmission points such as base stations of different cells, which are geographically separated from each other, cooperatively transmit data to a same terminal through a physical downlink shared channel (PDSCH) or jointly receive data from a same terminal through a physical uplink shared channel (PUSCH). With the CoMP technology, an edge user equipment is configured to use the same time-frequency resource of multiple base stations of neighboring cells. The multiple base stations simultaneously transmit the same downlink data to the edge user equipment to improve spectrum utilization of the edge user equipment.
The CoMP transmission technology is generally used in combination with a beamforming technology for co-frequency networking. On reception of uplink data from a UE, each of the base stations estimates a downlink channel condition using a dedicated adjustment reference signal which is pre-negotiated with the UE and an uplink channel condition, encodes downlink data using the downlink channel condition and transmit the encoded downlink data to the UE. On reception of the downlink data, the UE decodes the downlink data using the dedicated adjustment reference signal to obtain the downlink data transmitted by the base station.
The co-frequency networking implemented using the CoMP transmission technology in combination with the beamforming technology is only applicable to a unicast UE, that is, it is only applicable to a case where a base station transmits downlink data to one UE. The base station estimates the downlink channel condition with the beamforming technology using the dedicated adjustment reference signal and the uplink channel condition on which the UE transmits the uplink data to the base station. However, in a trunking service system, the base station transmits downlink data to multiple UEs. In a case where the base station estimates the downlink channel condition with the beamforming technology, the base station can estimate the downlink channel condition using only the uplink channel condition on which one UE transmits the uplink data to the base station. The base station encodes the downlink data using the estimated downlink channel condition and transmits the encoded downlink data to multiple UEs. In this case, only the UE that provides the uplink channel condition to the base station can decode the downlink data at a high accuracy rate using the dedicated adjustment reference signal, while the other UEs decode downlink data at a high error rate. Therefore, the co-frequency networking implemented using the CoMP transmission technology in combination with the beamforming technology is not applicable to the trunking service. In the conventional technology, there is no co-frequency networking technology that can be implemented in the trunking service.